Engine complaints by model year
Which parts fail
Components named in complaints (engine, cooling system, oil leaks, timing chain, exhaust).
Mileage when the problem started
What owners report
I own a 2003 Diamante Mitsubishi. The problem started with a check engine light coming on, fogging the window with a fowl toxic smell then the car would not hardly move out gear. I was told that the car's heater core leaked onto the computer which caused the transmission relay to short out do to the computer failing. The computer was still under warranty at 78,000 miles but I still had to pay for the new computer system because I was told that it was the heater core that caused the computer to fail. This is such a poor design! The computer should have been protected in such a case...funny thing it is now that I have had to replace a heater core, a computer and a transmission relay at a cut wrenching cost of $3,675.58. I wrote a letter to the president of north America Mitsubishi that the heater core should be a recall but to no avail. …
This is a Mitsubishi Diamante 2003 es. I'm experiencing a sweet smell of anti-freeze inside the car as soon as I turn on heating. Anti-freeze contains ethylene glycon and the fumes are highly toxic. Fixing the heater core will cost $1300. I am filing this complaint to ascertain that this is a very very common problem in Mitsubishi Diamante and Mitsubishi motors should be aware of three main risk associated with this: (1) the defect exposes customers to unusual level of toxic ethylene glycol which should not exceed 10-25 ppm levels (consult msds for ethylene glycol) (2) the leak can affect the car's microprocessor and poses a severe hazard for drivers. (3) faulty heater core makes the visibility difficult due to fogging of windshield thus putting the driver at greater risk. I will eventually fix the problem by spending $1300 if Mitsubishi refuses to issue a recall. …
Tl* the contact owns a 2002 Mitsubishi Diamante. The contact stated that while driving at 75 MPH, the contact attempted to brake but the brakes failed to respond without any warnings. The vehicle crashed into a passenger van. The vehicle was destroyed. The contact mentioned that two months prior to the failure the check engine light had illuminated. The vehicle was taken to an independent mechanic for diagnosis and was informed that the vehicle misfires, needed spark plugs, a fuel pump, a fuel injector, an EGR valve, and the engine surged erratically. The failure and current mileage was 140,000. Updated 12/06/12 updated 12/6/2012
This heater core leaks directly over computers which control the engine - and could cause it to act unpredictably or cut out altogether when driving. * anti-freeze contains ethylene gylcol which can cause serious respiratory damage * the leaking anti-freeze causes a film to form on the windshield, which can cause the windscreen to fog up suddenly, obscuring the view of the road and potentially causing a collision it will cost me more than 900.00 to repair this item, plus the cost to replace my carpet and to clean the interior of my vehicle. Plus I do not know if I will everget rid of the smell and this will most likely lower the resale value costing me even more in the long term.I would expect this kind of thing to happen to a car that is more than 10 years or old. …
My heater core went on my automobile. The car is a 2001 Mitsubishi Diamante which has 50,000 miles on it. The problem started when the car had 45,000 miles on it, but I didn't know it was the heater core until later on. The dealer had the car for 2-l/2 days for a job that was 6.9 hours. I was told that the box that the core was in was either broken or couldn't be shut, but then they were able to close it, fix it I hope. I was told by another mechanic that it could have been the o-ring and that they had a car the same year with the same problem, possible recall. The dealer did a shabby job in replacing my dash board, I have 3 screws that I found on the floor, my glove compartment has a screw missing, none of which I have in my possession fits the missing screw hole. When I picked up the car, the steering column came apart in my hands and so they took it back in to fix. …
My car is making me sick. I purchased my car in aug. 2001 and began to notice a smell in the car and fume closely resembling that of radiator coolant. The car was assesed by a Mitsubishi district manager and service personnel from my dealer and deemed to be sound. In the mean time I have suffered with runny eyes and intermittent paralysis in the right side of my face dependent on the amount of time spent in the car. I have contacted Mitsubishi numerous times about this and received no assistance. In November 2004 I noticed an increase in this smell and fogging problems of the interior windows. I took the car to the dealer telling them that I believed the problem was with the heater core. I ascertained this information through internet research dealing with Mitsubishi Diamante defects and problems. …
The fumes of antifreeze fogged up the windows severely, reducing visibility of the driver. It was raining one night and my windows all of a sudden got foggy. I turned on the defroster, which made my windows even foggier. The poor visibility caused me to run off the road into the grassy median. I was out of town when this occurred. In doing research on this problem I found that it was common all diamantes (92 -2001). In many cases, the driver is not aware that this is a severe problem. The antifreeze will started leaking on the passenger?s side area. Causing more strong smell of toxic antifreeze. I believe this to be a safety issue.
My wife and I noticed antifreeze odor coming in through vents. When our windows would fog, our defroster wouldn't work. Then our passenger side floor was soaked with antifreeze. We took the car to the dealer, our heater core was leaking. Cost was $1300 to repair. Mitsubishi should be held responsible!! Too many complaints.
Frequently asked questions
Which Mitsubishi Diamante years have engine problems?
By NHTSA complaints, the 2002 (38), 2003 (17), 2001 (14) and 2000 (7) model years. Engine complaints make up 31% of all complaints for the 2002.
Is there a recall for Mitsubishi Diamante engine problems?
No. NHTSA lists no engine & cooling recall for any Mitsubishi Diamante model year. A widespread problem may still be covered by an extended warranty or a manufacturer service bulletin, so ask a dealer.
At what mileage do Mitsubishi Diamante engine problems start?
Across all years, half of the complaints with a recorded mileage happened before about 67,000 miles; 15% happened before 50,000 miles.
What part fails most often?
Owners most often name the cooling system (38 mentions), followed by the engine (6).
Source: U.S. National Highway Traffic Safety Administration (NHTSA) — owner complaints through October 20, 2026, recalls and defect investigations; fuel economy from the EPA. Complaints are unverified reports and are not proof of a defect. How we rate model years.